This invention relates to a video signal processing apparatus for processing the video signal of high resolution, using a low frequency oscillator.
FIG. 1 shows the construction of the conventional video signal processing apparatus, and in this drawing, the reference number 1 shows CRTC (Cathode Ray Tube Controller), 2 a video memory, 3 a shift register, 4 an oscillator, 5 a counter, and 6 a monitor, respectively.
The CRTC 1 inputs a vertical synchronizing signal (Vsync) and a horizontal synchronizing signal (Hsync), and outputs a row address (RAO to RAn) and a memory address (MAO to MAn) to the video memory 2. The row address is counted as scan line number forming a pixel per one row, according to the clock outputted from the counter 5, and the memory address (MAO to MAn) is also counted according to the clock (CCLK). One pixel is formed as 40 dots.times.32 scan lines, the maximum character number on one picture is 32.times.32, that is, 1024 characters. Accordingly, the memory address (MAO to MAn) for displaying 1024 characters is to be counted in order to display 1024 characters each horizontal synchronizing signal period.
Therefore, the data written into the video memory 2 according to the memory address (MAO to MAN) and the row address (RAO to RAn) of the CRTC 1 is loaded in parallel from the video memory output terminal (DO to Dn) to the shift register 3 each clock of the load clock signal, and the shift register 3 converts the inputted parallel stream video data to the serial stream video data each clock of the dot clock signal and outputs them to the monitor 6.
Accordingly, if a high resolution corresponding to more than 1280.times.1024 is required, the high frequency clock oscillator is also required to provide the clock signal to the shift register. That is, in case of 1280 dots.times.1024 scan lines, the high frequency oscillator of 100 to 120 MHz is required. And also the fast processing apparatus is needed and this has a problems of using more expensive apparatus, and of causing a signal interference and noises.